Liquid crystal compounds have widely been used as a display material of TV sets, personal computers, watches, and so forth. Studies in recent years have revealed that those having a smectic liquid crystal phase exhibit charge transport properties, and their applicability as a charge transport material or a luminescent material in organic electroluminescent (EL) devices has been suggested. Liquid crystal compounds are classified into thermotropic and lyotropic liquid crystals according to the phase transition behavior, or classified into three categories: smectic, nematic, and cholesteric according to the molecular alignment.
The inventor of the present invention has previously proposed, as a result of his study, a charge transport method using a liquid crystal compound having a smectic liquid crystal phase as a charge transport material (see Patent Document 1), a liquid crystal compound exhibiting excellent charge transport properties without requiring photoexcitation (see Patent Document 2), and a liquid crystalline organic EL device having high carrier mobility (see Patent Document 3).
Noting that, in his latest work, the molecular alignment of organic EL materials affects electron/hole transport, the inventor proposed an electroconductive liquid crystal material that is obtained by co-depositing two distyrylbenzene compounds different in length of alkyl groups and displays a smectic liquid crystal phase on being heated to develop high charge transport properties (see Non Patent Document 1).    Patent Document 1: JP 2001-351786A    Patent Document 2: JP 2004-6271A    Patent Document 3: JP 2004-311182A    Non Patent Document 1: Japanese Patent Application No. 2004-354744 (Japanese Patent Application No. 2005-140800)